The invention relates to valves, and particularly, though not exclusively, to valves for use in controlling the functions of mine roof supports.
The operations of a modern hydraulic mine roof support involves the carrying out of a number of different functions such as the extension of a ram to push a coal conveyor away from a support into a newly cut part of a coal seam, the retraction of hydraulic legs of the support to free the support from the mine roof, the retraction of the said ram to draw the support up to the newly positioned conveyor, and the extension of the legs to reset the support to the mine roof.